New Reports of Downy Mildew on Pumpkins and Cucumbers in Ohio

Downy mildew symptoms on untreated pumpkin leaves in Clark County, OH. Photo by Jim Jasinski.

Downy mildew was reported for the first time in pumpkins in Ohio in Clark County at the OSU Western Agricultural Research Station. Jim Jasinski noticed possible symptoms in an untreated control in a pumpkin research trial as many as 10 days ago, but the disease did not progress rapidly in last week’s heat. However, we were able to confirm downy mildew today. This is so far the furthest north that downy mildew has been found and reported on pumpkins or squash in the US. It is likely caused by Clade 1 of the pathogen, which comes from SE US and is more aggressive on pumpkins, squash and watermelons than other cucurbits.  Pumpkin and squash growers throughout Ohio should apply appropriate protectant fungicides now and scout fields thoroughly. Growers in Clark County should begin a fungicide program with downy mildew-effective fungicides now.

In the last week or so Ohio Master Gardener Volunteers in our Citizen Science project to monitor this disease have also reported downy mildew on cucumbers in Belmont, Jefferson and Geauga counties. Rainy or cloudy weather and moderate temperatures are expected this week in much of Ohio – these conditions are ideal for downy mildew.

For all cucurbits: If favorable conditions for downy mildew persist and downy mildew is present in your area, add effective fungicides shown in green in the Table to the spray program. Tank mix with a protectant fungicide, alternate fungicides with different modes of action (FRAC codes) and follow the label restrictions and requirements. Shorten the application interval to 7 days under favorable weather for downy mildew.

  1. Forum, Presidio, Quadris, Zampro and Revus are not recommended. Curzate may be moderately effective in some locations.
  2. Follow this blog, Twitter @OhioVeggieDoc or the Cucurbit Downy Mildew IPM PIPE for downy mildew reports.

Map of US counties with cucurbit downy mildew reports.

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